The present invention relates to rayon fibers superior in deodorization performance and to a method for producing the rayon fibers.
Deodorization treatment has been conventionally applied to rayon fibers used as wadding and rayon fibers for clothing in order to prevent quilts or clothes from offensive smelling. The deodorization treatment has been also applied to rayon fibers used in carpet, wall cloth, or the like, in order to prevent a room from offensive smelling by adsorbing it into the carpet or the like.
As one of such deodorant rayon fibers, a deodorant rayon fibers containing fine grains of activated charcoal, into which metal complex of phthalocyanine is adsorbed, in a matrix of the rayon fiber are known (the Japanese Patent Publication (unexamined) No. 300769/1988). This deodorant rayon fibers transforms odor molecules into odorless molecules (odorless components) through a chemical reaction between the metal complex of phthalocyanine adsorbed by the fine grains of activated charcoal and the odor molecules. It is to be noted that, in this known art, the fine grains of activated charcoal are used just for carrying the metal complex of phthalocyanine, and not for adsorbing the odor molecules. This is because when the fine grains of activated charcoal are contained in the matrix of the rayon fiber, micropores of the fine grains of activated charcoal are coated or covered by cellulose and the power for adsorbing the odor molecules is almost lost. In other words, when such a type of deodorant as adsorbing the odor molecules into micropores (activated charcoal is typical) is implanted (contained) in the matrix of the rayon fiber, its deodorization performance is lost. As a result, it is impossible to give any deodorization performance to the rayon fibers. This has been a common technical sense in the field of art.
However, the inventors have found that a specific deodorant among the deodorants of the type adsorbing the odor molecules into the micropores does not substantially lose its deodorization performance even if the deodorant is implanted in the matrix of the rayon fiber. Moreover, the inventors have also unexpectedly found that deodorization performance is further improved for a certain kind of odor components as compared with the deodorization performance achieved by using the specific deodorant alone, and that the specific deodorant produces minus ions under specific conditions. (It is usually said that the more minus ions exist, the more favorable environment is provided for human body.)
The present invention was made on the basis of the foregoing discoveries.
The present invention relates to deodorant rayon fibers implanting fine grains, which are produced by milling white charcoal made by carbonizing an oak, in a matrix of the rayon fiber. Scratch hardness of the white charcoal is prefferably more than 15 degree. The degree of the scratch hardness is set on the basis of the scratch hardness of steel and lead. That is, the scratch hardness of steel is 20 degree, and the lead is 1 degree.
It is preferable in the present invention to use xe2x80x9cBinchotanxe2x80x9d charcoal which is a kind of white charcoal. xe2x80x9cBinchotanxe2x80x9d charcoal is a white charcoal made in Japan. xe2x80x9cBinchotanxe2x80x9d charcoal is produced by carbonizing xe2x80x9cUbamegashixe2x80x9d which is a kind of oak. Scratch hardness of xe2x80x9cBinchotanxe2x80x9d charcoal is simillar to that of steel or harder than steel.
In general, a viscose rayon fiber is used as the rayon fiber, and it is also preferred to use a cuprammonium rayon fiber or an acetate rayon fiber as the rayon fiber.
The most significant characteristic of the present invention is that fine grains produced by milling white charcoal, prefarably xe2x80x9cBinchotanxe2x80x9d charcoal, are used as a deodorant to be implanted in the matrix of the rayon fiber. It is considered that once using the fine grains of white charcoal, deodorization function is not easily deteriorated even if the fine grains are implanted in the matrix of the rayon fiber by the following reasons. The white charcoal has a property of being harder than activated charcoal and black charcoal. Espesially, the xe2x80x9cBinchotanxe2x80x9d charcoal is simillar to or harder than steel in hardness, therefore cannot be cut with a saw, and the teeth of the saw will be nicked instead of cutting the xe2x80x9cBinchotanxe2x80x9d charcoal. Accordingly, when such a hard white charcoal is mlled into fine grains by applying shock and friction using a hammer mill, a ball mill or the like, the fine grains do not form spheres with smooth surfaces, but their configurations become irregular with recessions and projections. When a large quantity of such fine grains of the white charcoal is implanted in the matrix of the rayon fiber, the projections on the surfaces of the fine grains are in contac with the surface of the rayon fiber at a large number of points xe2x80x9caxe2x80x9d as shown in FIG. 1. (FIG. 1 is a schematic view showing a cross section of the deodorant rayon fiber). At these points xe2x80x9caxe2x80x9d, the projections of the fine grains are sometimes exposed. In other cases, the projections are not originally exposed, but when the surface of the rayon fiber is rubbed, the surface of the rayon fiber is gradually damaged, and consequently, the projections of the fine grains are finally exposed. It is therefore considered that odor components are taken or adsorbed into the fine grains through these exposed portions, whereby the deodorization function is performed.
It is considered that this is the very reason why the deodorization performance of the rayon fibers, in the matrix of which the large quantity of fine grains is implanted, is not easily deteriorated.
The deodorant rayon fibers according to the invention are generally produced as described below. First, the white charcoal is prepared and milled to obtain a large quantity of fine grains of the white charcoal. Any of publicly known methods can be used. It is, however, preferred to use a two-stage milling method in which rough milling is performed at first stage, and fine milling is performed at next stage. The most preferable process method is to use the two-stage milling method in which the rough milling is performed by dry milling, and wet milling performs the fine milling. Any of publicly known milling machines can be used. It is, however, preferred to use a hammer mill, a roll crusher, or the like in the rough milling, and use a ball mill, a tower mill, or the like in the fine milling.
Grain diameter of the fine grains of the white charcoal can be any value as far as the grain diameters are small enough to be implanted in the matrix of the rayon fiber. It is, however, preferred that at least 95% of the large quantity of the fine grains is less than 1.0 xcexcm in grain diameter. If less than 95% of the fine grains are less than 1.0 xcexcm in grain diameter, when adding and mixing the fine grains into viscose solution, there arises a possibility that the viscose solution increases its viscosity, eventually resulting in occurrence of gelation. In addition, distribution of the grain diameters of the fine grains can be measured using a coal counter or the like. The large quantity of fine grains obtained in this manner is then dispersed in water to produce water dispersion. In the dispersion of the fine grains in water, it is preferred to use a suitable dispersant such as surfactant, but it is not always necessary to use a dispersant Furthermore, in case that the fine grains are obtained through the wet milling using water (any dispersant such as a surface-active agent is contained therein in some cases), those fine grains are already dispersed in water. Therefore, it is also preferred to use them as they are. Rate of the fine grains in the water dispersion is preferably in the range of 5 to 80 weight percent. If the ratio is less than 5 weight percent, number of the fine grains implanted in the matrix of the rayon fiber tends to be insufficient. On the other hand, if the ratio is more than 80 weight percent, obtaining the water dispersion in which the fine grains are stably dispersed tends to be difficult,
With respect to the viscose solution into which the water dispersion are added and mixed, any publicly known viscose solution can be used for producing viscose rayon fibers. More specifically, it is preferred to use the viscose solution in which the ratio of contained cellulose is approximately in the range of 7 to 10 weight percent, and the ratio of alkali such as caustic soda to the cellulose is approximately in the range of 50 to 80 weight percent. It is preferred that the viscose solution optionally contains any additional agent such as various kinds of metallic salts and antistatic agents. The water dispersion produced by dispersing the large quantity of fine grains of the white charcoal can be added and mixed into the viscose solution at any time before spinning. It is, however, most preferable to add and mix the water dispersion just before spinning. With the passage of a long time after adding and mixing the water dispersion, the fine grains tend to cohere or sediment, whereby maintaining the state of being uniformly mixed becomes difficult. With respect to the adding method, any publicly known method can be adopted. It is, however, preferred to quantitatively and continuously add the water dispersion into the viscose solution usin an injection pump.
It is possible to add any quantity of fine grains of the white charcoal into the viscose solution. In general, it is preferred to add the fine grains to the weight of the cellulose in the viscose solution in the range of 1 to 40 weight percent, more preferably, 5 to 20 weight percent. If the adding quantity of the fine grains is less than 1 weight percent, the quantity of the fine grains implanted in the matrix of the rayon fiber is insufficient, and there is a possibility that the deodorization function is not sufficiently performed. On the other hand, if the adding quantity of the fine grains is more than 40 weight percent, there arises a tendency of lowering in spinning characteristic, and easily dropping out of the fine grains from the obtained deodorant rayon fibers. There may further arise a tendency of deteriorating the physical properties such as strength and elongation of the deodorant rayon fiber.
After obtaining a mixture by adding and mixing the water dispersion to the viscose solution, spinning is performed in the same manner as that in producing the rayon fibers. More specifically, the mixture is extruded from a spinning nozzle into coagulating solution (temperature of the solution is approximately in the range of 40 to 50xc2x0 C.). The coagulating solution contains 80 to 120 g/l of sulfuric acid and 50 to 360 g/l of sulfate of soda as main components. The mixture extruded into the coagulating solution is transformed into regenerated cellulose and coagulates, and then is optionally subject to drawing, thus rayon fibers being obtained. In this invention, since the fine grains exist into the mixture, the deodorant rayon fibers, in which the large quantity of fine grains is implanted in the matrix of the rayon fiber, are obtained by the method described above.
The deodorant rayon fibers obtained in this manner are used in the form of long fibers or short fibers of any desired fiber length. A deodorant yarn is obtained by spinning those deodorant rayon fibers. Instead of obtaining such yarn, it is possible to integrate the deodorant rayon fibers to form them into deodorant wadding, or to obtain a deodorant non-woven fabric by conbining the deodorant rayon fibers each other by any suitable means. Furthermore, by knitting or weaving the deodorant yarns obtains deodorant fabric. The deodorant non-woven fabric etc. are suitably applied to publicly known uses as a material for, for example, a clothing, a bed sheet, a pillowcase, a blanket, a carpet, a wall cloth, a cloth for stuffed toys, a curtain, a covering cloth, a cushion cover, and a lining cloth for vehicles.
Other objects, features and advantages of the invention will become apparent in the course of the following description with reference to the accompanying drawings.